The Fusselman Formation is a geologic formation in westernmost Texas and southern New Mexico. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

dating back to the early Silurian period.

Description

The formation consists mostly of medium to dark gray massive

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

. It has a light and dark banded appearance due to alternating beds of light gray peritidal laminated

carbonate mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...

and dark gray cherty wackestone or packstone containing abundant corals. The total thickness is over in the Florida Mountains but the formation varies greatly in thickness. The formations

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

overlies the

Montoya Group The Montoya Group is a group of geologic formations in westernmost Texas and southern New Mexico. It preserves fossils dating back to the late Ordovician period.Richardson 2008Pope 2004 Description The group consists mostly of dolomitePray ...

and is overlain by the Onate Formation. The upper contact shows that the area was tilted and eroded prior to the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

. The formation is divided into the Chamberino, Flag Hill, and Crazycat members in the Sacramento Mountains. Extensive dolomitization of the formation has obscured its primary depositional fabric and made interpretation of its depositional environment difficult.

Fossils

The formation is relatively poor in fossils compared with the underlying

El Paso Formation The El Paso Formation is a geologic formation that is exposed from the Permian Basin of New Mexico and Texas to southeastern Arizona. It preserves fossils dating back to the Ordovician period. Description The formation is composed of gray chert ...

. However, it contains fossils of pentamerid brachiopods, corals, and

stromatoporoid Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Ordovician through the Devonian. They were especially abundant and important reef-formers in the Silurian and most of the Devonian.Stock, C.W. 2001, Stro ...

s. These include the corals ''Cyanthophyllum'', ''

Favosites ''Favosites'' is an extinct genus of tabulate coral characterized by polygonal closely packed corallites (giving it the common name "honeycomb coral"). The walls between corallites are pierced by pores known as mural pores which allowed transfer ...

'', ''

Halysites ''Halysites'' (meaning ''chain coral'') is an extinct genus of tabulate coral. Colonies range from less than one to tens of centimeters in diameter, and they fed upon plankton. These tabulate corals lived from the Ordovician to the Devonian (fro ...

'', and ''

Heliolites ''Heliolites'' is a large and heterogenous genus of extinct tabulate corals in the family Heliolitidae. Specimens have been found in Ordovician to Devonian beds in North America, Europe, Africa, Asia, and Australia. The genus is particularly abu ...

'' and the

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

''Hormatoma''.

Economic geology

The uppermost part of the formation shows significant

barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

- fluorite and base metal

mineralization Mineralization may refer to: * Mineralization (biology), when an inorganic substance precipitates in an organic matrix ** Biomineralization, a form of mineralization ** Mineralization of bone, an example of mineralization ** Mineralized tissues are ...

, where migrating fluids are trapped by the overlying impermeable

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

formations.

History of investigation

The name was first used by G.B. Richardson in 1908 for outcrops in Fusselman Canyon in the Franklin Mountains. It was divided into members in the Florida Mountains by Kottlowski and Pray in 1967.

Footnotes

References